1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device in which a liquid crystal panel and a circuit board for driving the liquid crystal panel are electrically connected through a flexible printed circuit.
2. Description of Related Art
A liquid crystal display device is known in which a liquid crystal panel and a PCB (Printed Circuit Board) for driving the panel are electrically connected to each other through a flexible connector such as an FPC (Flexible Printed Circuit). In recent years, it has become common to use an arrangement known as COF (Chip on Film) in which an integrated circuit such as a liquid crystal driving LSI (Large Scale Integrated Circuit) chip is mounted on a flexible printed circuit as disclosed, for example, in Japanese ]Utility Model Laid-Open No. 1-88928.
FIG. 10 is a perspective view of an example of a known liquid crystal display device which uses COF technology. Referring to FIG. 10, the liquid crystal display device has a liquid crystal panel 1 held by a flat rectangular framework 2 made of a material such as aluminum or a cold-rolled steel sheet. The framework 2 is fixed at a plurality of portions thereof to a case (not shown) made of plastic, by being secured to the case with securement tabs 2a (which are inserted into slots in the case, and then bent from behind) or by means of screws so that the framework presses against the peripheries of at least two sides of the liquid crystal panel (for example, the left and right sides or the top and bottom sides of panel 1 as shown in FIG. 10). The liquid crystal panel 1 and the framework 2 are integrally held together with the case (not shown) by the above-mentioned pressing force, thus forming the liquid crystal display device.
In the construction described above, it is necessary to distribute as many attachment points (i.e., using tabs 2a or screws) as possible as uniformly as possible on framework 2 as shown in FIG. 10 in order to avoid breakage of the liquid crystal panel 1 which may otherwise be caused by local concentration of stress on the liquid crystal panel 1. Consequently, the degree of freedom of the structural design is undesirably limited and the number of steps in the assembly process is increased, thus lowering the production efficiency.
In general, a liquid crystal display device undergoes assembly and disassembly a plurality of times for the purpose of maintenance and periodic inspection during its lifetime. Therefore, when securement of the liquid crystal panel relies upon securement tabs 2a, it is necessary that the material of the framework 2 is capable of enduring several cycles of flexing (i.e., due to bending and straightening of tabs 2a). To meet this requirement, the framework 2 is made of, for example, a cold-rolled steel sheet having a thickness of 0.6 mm or greater. When screws are used as a means for securing the liquid crystal panel, the material of the framework 2 must be capable of sustaining the tightening torque exerted on the fixing screws. However, the number of possible positions where the screw holes can be formed are limited. Therefore, in order that the liquid crystal panel is pressed uniformly, securement tabs 2a are usually required in addition to screws because fixing by screws alone cannot provide sufficient fixing effect. This essentially requires that a metal is used as the material of framework 2.
In order to simultaneously press at least two sides of the liquid crystal panel 1, the framework 2 essentially has a planar rectangular form with outside dimensions sufficiently greater than those of the liquid crystal panel 1, as can be seen from FIG. 10. Consequently, the size and weight of the framework 2 are large, with the result that the overall weight of the entire liquid crystal display device is increased.
When a metal is used as the material of the framework 2 for the reasons stated above, it is necessary to provide a suitable electrical insulation member for electrically isolating the metallic framework 2 from a circuit board (not shown) or from a flexible printed circuit (not shown) which is usually disposed in close proximity of the framework 2. Provision of such an electrical insulation member undesirably increases the number of steps in the assembly process and increases the outside dimensions of the framework 2 by an amount corresponding to the space required for accommodating the electrical insulation member, with a consequence that the overall size of the liquid crystal display device is increased even further.